Elgg activates its cron handler when particular cron pages are loaded.
As an example, loading http://example.com/cron/hourly/ in a web browser
activates the hourly hook. To automate this, cron jobs are setup to hit those
pages at certain times. This is done by setting up a crontab which is a
configuration file that determines what cron jobs do and at what interval.

The crontab needs to specify a script or command that will hit the Elgg cron pages.
Two commonly available programs for this are GET and wget. You will need
to determine the location of one of these on your server. Your crontab also needs
to specify the location of your website.

In the above example, change the ELGG and GET variables to match you server setup.
If you have SSH access to your Linux servers, type crontab-e and add
your crontab configuration. If you already have a crontab configured, you will have to
merge Elgg information into it. If you don’t have SSH access, you will have to use
a web-based configuration tool. This will vary depending on hosting provider.

If you choose the wget utility, you might want to consider these flags:

--output-document or -O to specify the location of the concatenated output file.
For example, under Debian: /usr/bin/wget--output-document=/dev/null. If you don’t do
that, a new file will be created for each cron page load in the home directory of the cron user.